Skin rejuvenation is a one of the most popular cosmetic procedures.
Skin tissue consists of an outer epidermal layer overlying a dermal layer that is in contact with a layer of subcutaneous adipose tissue. Aging of the skin results in appearing such aging signs as wrinkle, rough skin texture and discoloration.
Fractional ablation of part of the skin during a few treatments results in skin resurfacing with minimal risk of skin damage. The fractional skin ablation results in localized heating and ablation of the skin area that is in exposed by applied energy. Ablation of the skin promotes skin resurfacing while untreated skin between the ablation dots promotes faster healing of the tissue. Damaged tissue is evacuated from the body by the lymphatic system.
The most popular method for fractional skin resurfacing is laser fractional ablation where laser energy focused onto the small spot of skin which is less than 1 mm and ablate it. CO2, Erbium, Diode and Nd:Yag lasers in infrared spectrum range are used for this purpose. Laser beam is replaced with the scanner. The U.S. Pat. No. 7,090,670 describes array of laser beams used for paternal ablation of the skin.
The other method of fractional skin ablation is based on RF energy. Patent application US 2010/0185194 describes array of needles penetrating into the skin and creating fractional thermal ablation of the tissue.
The main limitation of the above described methods of thermal skin ablation is poorly controlled thermal zone around the ablated area. Heat transfer from the ablation zone may result in overlapping of thermal zones and potential skin scarring and dischromia especially for darker skin.
The alternative method of skin ablation is irreversible electroporation of the soft tissue that causes non-thermal damage of the cells.
U.S. Pat. No. 5,810,762 describes a device with support for treating target within the human body.
U.S. Pat. No. 6,795,728 describes a device with needles having an isolated shaft and a conductive tip which are inserted into the body to deliver HV into the fat tissue.
U.S. Pat. No. 6,892,099 describes a use of a long electrical pulse with duration above 10 microseconds for non-invasive treatment of tissue volume with fat. The main limitation of this invention is electrical shock associated with application of electrical voltage with pulsed duration longer than 10 microseconds. This strong effect on nerves inside the body is potentially dangerous and makes treatment not tolerable without general anesthesia.
U.S. Pat. No. 6,697,670 tries to overcome this limitation by combining HV pulse with a nerve stimulating signal but this effect is difficult to control.
The other invention described in the U.S. Pat. No. 6,326,177 describes a method of creating cell apoptosis using short pulses from 100 ps up to 1 microseconds. Using the short pulses allows the avoidance of nerve effect and makes the treatment potentially more friendly. From the other side, using short pulses require higher electric field strength above 10 kV/cm that creates electrical breakdown in the air. Such breakdown generates plasma that burns the skin and makes the use of high electric field pulses non-invasively not practical.
In spite of the attractiveness of electroporation technology, all of the above mentioned limitations resulted that there is no commercially available device in the market for irreversible electroporation.
The main limitations of electroporation are:                The use of HV that may create arcing around electrode and damage the skin surface;        Using long pulse or multiple pulses with single polarity may create risk of electrical shock; and        In addition, generation of short pulses with amplitude of a few kilovolts has many technical challenges.        
HV electrical pulses are also used for sterilization destroying bacteria. In article “Electrical Sterilization of Juice by Discharged HV Impulse Waveform”, Hee-Kyu Lee, American Journal of Applied Sciences 2 (10): 2076-2078, 2006 has shown that survivability of the cells is a strong function of temperature and increase of temperature from 30° C. to 40° C. may provide the same survivability at twice the lower electric field strength.
The inventor herein believes that a non-invasive device for cosmetic treatment should satisfy to the following requirements:                Pulse duration should not exceed 10 microseconds to avoid electrical shock and risk associated with it; and        Pulse amplitude should be high enough to create irreversible damage to the cells but below breakdown threshold in the air over the skin surface.        